Joichiro Moriyama

Measurements on galvanic cells involving solid-sulphide electrolytes

Abstract It has been shown that emf measurements on galvanic cells involving solid-sulphide electrolytes may yield valuable thermodynamic data. CaSY2S3 and CaSZrS2 solid solutions were expected to satisfy the conditions as solid electrolyte. Emf measurements on the cells MoMo2S3(3 + s)/electrolyte/CuCu2S(1 + 1) (I), MoMo2S3(s + s)/electrolyte/Fe FeS(s + 1) (II), MoMo2S3(s + s)/electrolyte/WWS2(s + s) (III), WWS2(s + s)/electrolyte/CuCu2S(1 + 1) (IV), and WSW2(s + s)/ electrolyte/FeFeS(s + 1) (V) have been made using sulphide sensors in the temperature range 1000–1285°C. Observed emf values were compared with those calculated from the H2H2S gas equilibrium investigations. The sensor tubes were also dipped into liquid copper with sulphur concentration from 0.43 to 1.06 at% 1180–1312°C and the emf data were checked by the values deduced from the gas equilibrium experiments.

Deoxidation of high-melting-point metals and alloys in vacuum

Through melting, refractory metals and alloys are becoming important for use as structural materials. Vacuum-melting is considered to be able to provide high-purity ingots because of its purifying effect, particularly the effect of evaporation deoxidation via volatile oxides. Thermodynamic calculation leads us to predict a limited possibility for deoxidizing Ti, Zr, Hf, a good possibility for Mo and W, and an intermediate possibility for V, Nb, and Ta. The sponges of these metals containing oxygen were degassed under high vacuum at temperatures below or over the melting point, and the change in oxygen content was measured as a function of time. The observed rates of purification agreed well with the thermodynamically estimated deoxidizing tendencies. Kinetic analysis of the degassing curves obtained for the Nb-O, Ta-O, Mo-O, and W-0 alloys showed that the rate-determining step was the diffusion of oxygen in the metal or the recombination of oxygen with the base metal atoms and the transfer of the molecules into the vacuum. If carbon was present in the metal, the oxygen liberation was considerably accelerated. However, an excess of oxygen to carbon was necessary for the carbon level to be sufficiently lowered at the same time.

Oxygen pressure measurements of silica saturated Fe-O-SiO2 melts by the emf method using zirconia solid electrolyte

The thermodynamic properties of silica-saturated iron silicate slags have been studied from oxygen partial pressure measurements using a solid electrolyte galvanic cell. The oxygen activity in molten silver bath equilibrated with iron silicate slags was determined by the following cell type, Pt, Ni-NiO/O=/slag-Ag(O), LaCrO3, Pt at temperatures between 1473 and 1573 K for the slags ranging in compositions from iron saturation to magnetite saturation. The oxygen partial pressures obtained in this investigation were in good agreement with those given by the previous study using the CO-CO2 gas equilibrium method. The data showed that the Fe+++/Fe++ ratio is proportional toPo2¼

A thermodynamic study of silica-saturated iron silicate slags in equilibrium with liquid copper

The thermodynamic properties of silica-saturated iron silicate slags in equilibrium with liquid copper have been studied from oxygen partial pressure measurements in the temperature range from 1490 to 1580 K by means of a solid electrolyte galvanic cell. The following cells were used: Pt, Ni-NiO/O=/slag-Cu(l), Cr2O3, Pt; Pt, Fe-FeO/O=/slag-Cu(Fe sat.), Fe. A strong correlation was found between oxygen pressure and the copper content of the slag; the copper content increased from less than 1 pct near iron saturation to about 4 pct at an oxygen partial pressure of 7.2 x 10−3 Pa. A similar correlation was found between the ferric iron/total iron ratio and the oxygen pressure. The oxygen content in liquid copper decreased with increasing iron content in liquid copper and increased slightly near iron saturation. This behavior could be explained qualitatively by using the standard free energy of formation of FeO and the activities of components.

Galvanic cells involving solid-sulphide electrolytes for the determination of sulphur chemical potentials at elevated temperatures

Abstract It has been shown that emf measurements on galvanic cells involving solid-sulphide electrolytes may yield valuable thermodynamic data. CaS is believed to be Ca 2+ ion conductor, the electrical conductivity of which is, however, very low. Doping the CaS with Y 2 S 3 or ZrS 2 results in a cation substitution with the creation of cationic vacancies and thus in an increase in the conductivity. The CaS2wt%Y 2 S 3 and CaS2wt%ZrS 2 solid solutions were expected to satisfy the conditions as electrolyte, and the cells were constructed using the two-phase mixture electrodes, Mo( s ) + Mo 2 S 3 ( s ), W( s ) + WS 2 ( s ), Cu(1) + Cu  S(1) and Fe( s ) + Fe  S(1). The cell performance was successful at 1273–1573 K. The observed emf values were in good agreement with those calculated from known thermodynamic data. These results may indicate the usefulness of solid-sulphide electrolytes for the determination of sulphur chemical potentials at elevated temperatures.